We concentrate on the critical distinction between immortal early embryonic cells and mortal differentiating derivative cells. We apply large-scale systematic methodology "embryogenomics" to the study of preimplantation development - the process of fertilized egg gradually losing its totipotency. In our previous work, we have completed the microarray-based global expression profiling of all preimplantation stages in mouse, which revealed and characterized the distinctive patterns of maternal RNA degradation and two major transient waves of de novo transcription. The first wave corresponds to zygotic genome activation (ZGA); the second wave, named mid-preimplantation gene activation (MGA), precedes the dynamic morphological and functional changes from the morula to blastocyst stage. We propose a cascade of gene activation from maternal RNA/protein sets to ZGA gene sets and thence to MGA gene sets ("waves of gene activation hypothesis"). Among the candidate genes identified in this study, we have selected and studied one novel gene encoding a zinc finger binding protein, which shows a transient expression in 2-cell embryos. The functional analysis of this gene, including a gene disruption study, is underway.